var preloaded = new Array();
function preload() {
  var imgarray = preload.arguments;
  for (i = 0; i < imgarray.length; i++) {
    preloaded[i] = new Image();
    preloaded[i].src = imgarray[i];
  }
}

var lastswitched = new Array(2);
function switchimg(imgName,imgSrc) {
  if (switchimg.arguments.length) {
    lastswitched[0] = imgName;
    lastswitched[1] = document.images[imgName].src;
    document.images[imgName].src = imgSrc;
  }
  else { document.images[lastswitched[0]].src = lastswitched[1]; }
}